1. Field of Invention
The present invention relates generally to insoluble branched polyphosphonates and methods for their preparation. It also relates to polymer compositions including these insoluble polyphosphonates and articles produced therefrom.
2. Description of Related Art
Polyphosphonates exhibit excellent fire resistance (e.g., U.S. Pat. Nos. 2,682,522 and 4,331,614). Generally, linear polyphosphonates are produced by melt condensing a phosphonic acid diaryl ester and a bisphenol using a metal catalyst (e.g., sodium phenolate) at high temperature (e.g., U.S. Pat. No. 2,682,522). However, this approach produced low molecular weight polyphosphonates that exhibited poor toughness.
To improve toughness, methods for producing branched polyphosphonates by transesterification were developed. In the transesterification reaction, a phosphonic acid diaryl ester, bisphenol, a branching agent such as tri or tetra phenol or phosphoric acid ester and a catalyst, such as sodium phenolate are combined and reacted in the melt, usually in an autoclave (e.g., U.S. Pat. Nos. 2,716,101; 3,326,852; 4,328,174; 4,331,614; 4,374,971; 4,415,719; 5,216,113; 5,334,692; and 4,374,971). This approach was successful in producing high molecular weight polyphosphonates that exhibited improved toughness, but processability was sacrificed. For example, branched polyphosphonates with a number of average molecular weights (Mn) of from 11,000 g/mole to as high as 200,000 g/mole with polymer dispersities of less than 2.5 have been described. However, these polyphosphonates exhibited high melt viscosities, lack of hydrolytic stability and exhibit a haze in the material. Consequently, the combination of properties exhibited by these polyphosphonates are not sufficient for general acceptance in the marketplace.
More recently, a method to synthesize branched polyphosphonates with an improved combination of properties such as higher Tgs, better toughness and superior hydrolytic stability has been developed using a phosphonium catalyst such as tetraphenylphosphonium phenolate (TPPP) (U.S. Pat. No. 6,861,499). These polyphosphonates exhibit very high molecular weight, good melt processability and, depending on the reaction conditions used, can be soluble or insoluble. Unfortunately, TPPP has several disadvantages in that it is expensive and the reaction time required to make polymers using this catalyst is slower compared to sodium phenolate resulting in higher costs to produce polyphosphonates. In addition, TPPP is volatile under the reaction conditions and has to be added periodically to maintain a sufficient concentration.